74 THE WHITE PINE 



Fig. 6. 



Current annual increment. 

 Mean annual Increment. 



Since the mean annual increment at any time 

 is the average of all the current annual incre- 

 ment of previous years, it is evident that when 

 the latter falls below its own average, the aver- 

 age itself (or the mean annual increment) will 

 have passed its highest point, which will neces- 

 sarily be at the moment when both are equal. 

 Thus for White Pine on land of first quality the 

 mean annual increment, without bark, reaches 

 its highest point in the table at 70 years, with 

 a production of 98.6 cubic feet per acre. The 

 current annual increment for the same age is 

 100 cubic feet per acre. At 80 years these 

 values are 97.5 and 90 respectively. At some 

 year between these two there is a point at which 

 the mean annual increment rises from 98.6, and 



